The freezing temperature (i.e., melting point) of oil-and-fat feedstocks may vary over a significantly wide range, which results in a distribution of them in the state of from solid to liquid at ordinary temperatures, depending upon their composition. In general, oil-and-fat feedstocks partially crystallize at refrigerator temperatures (of from room temperature to about 0.degree. C.) to cause clouding or turbidity, and totally solidify at freezer temperatures (of lower than 0.degree. C., typically about -20.degree. C.). When emulsified food containing an ordinary liquid fatty oil, such as dressing and mayonnaise, is allowed to freeze and thaw, its emulsification state is broken, thereby causing the separation of an oil phase. Therefore, emulsified food such as mayonnaise is not used as a food material to be separately enclosed within the main package of frozen food such as frozen fries with batter. For the stone reason, it is difficult to produce custard cream and custard cream-containing food as frozen food.
So far as the present inventors know, no attempt has hitherto been known to improve the freezing resistance of oil-and-fat feedstocks.
As an oil-and-fat feedstock for enteral nutrient of patients suffering from hepatopathy or the like, there have hitherto been known SUS-type (1,3-disaturated-2-unsaturated) triglycerides having middle-chain fatty acid residues of 8 to 12 carbon atoms at the 1st and 3rd positions thereof and a long-chain unsaturated fatty acid residue with two or more unsaturated groups at the 2nd position thereof (see, e.g., JP-A 63-297342). It is also described that the oil-and-fat feedstock can be utilized in mayonnaise, dressing and the like because it is in liquid state at ordinary temperatures, although it is unknown whether this oil-and-fat feedstock can be used as a freezing-resistant oil-and-fat material (see also JP-A 63-297342). Further, it is disclosed that another SUS-type triglyceride, 1,3-didecanoyl-2-Canola glyceride is useful as an oil-and-fat feedstock for enteral or parenteral nutrient (see, e.g., JP-A 4-500971 ).
These conventional feedstocks are, however, unsatisfactory as a general-purpose edible oil-and-fat feedstock from an economical point of view because they are products with high purity for pharmaceutical use and many efforts are required for their purification.
It is well known that the melting point of oil-and-fat feedstocks has a tendency to increase with an increase in the chain length of their substituent fatty acid residues or in the degree of saturation. It is, however, difficult to predict the melting point of complex mixed fatty acid triglycerides. For example, even in case of trilinolenin (linolenic acid triglyceride) which is ordinarily supposed to have a low melting point, its melting point is merely -23.degree. C. Moreover, oil-and-fat feedstocks have a property of polymorphism; for example, triolein can take different forms, such as .beta.-form (m.p., 4.9.degree. C.), .beta.'-form (m.p., -12.degree. C.) and .alpha.-form (m.p., -32.degree. C.), so that it may cause crystal deposition even at relatively high temperatures such as about refrigerator temperatures.